>> EU united their currency from several individual ones and they are doing great...more countries are thinking about adopting Euro which rivals US dollars now

I am not sure EU is doing great when Switzerland has voted to limit freedom of movement of other EU nations into the country. There are few that will think EU is doing fine at this point based on the currency unification. Without EURO, Greece would have avoided its problems. They will simply devalue their currency. But with none, no instrument to play.

"Bitcoin is like the housing market before the bubble. It is irrational exuberance at the best"

Indeed, the recent peak in the market value of bitcoins and subsequent "crash" is typical of such a boom/bust cycle. Keep in mind that this has happened at least twice before (in mid 2011 and again early last year), both times starting from much lower levels. For those who were speculating on the market value of bitcoins, those proved to be good buying opportunities.

>>I guess in this case risk is high...but payoff is huge...what if the whole world adopts BitCoin?

That will not happen because the most effective tool for any economic strategy is the monetrary policy. That is one reason why currency union suffers. If you owe $30b to companies in your local currency, you have the power as government to devaalue your currency to get more money in the central bank to pay that off. When you lose that power, you are in trouble. I do not see why government will lose that tool to Bitcoin which they cannot manipulate.